The probe covers an estimated 280,000 vehicles. Five drivers alleged in complaints they couldn't steer the vehicles at all. Seven more cited a loss of power steering that required increased steering effort.
There was one report of a crash but no complaints of any injuries.
The agency says in a document posted Tuesday on its website that loss of steering control can be accompanied by messages to drivers indicating that the power steering assist has been reduced or disabled.
The document says investigators will look into how often the problem happens, manufacturing processes and the severity of the problem.
The probe is at least the sixth started by the agency into Tesla vehicles in the past three years. Investigators are looking into Teslas that can crash into parked emergency vehicles while running on the Autopilot partially automated driving system, emergency braking for no reason, suspension failures, steering wheels that can fall off, and front seat belts that may not be connected properly.
Messages were left Tuesday seeking comment from Tesla.
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